Current limiting circuit breakers



Aug. 4; 1970 A. BIANcHl EFAL CURRENT LIMITING CIRCUIT BREAKERS 7 Sheets-Sheet 2 Filed Jan. 30, 1968 wOT .v07

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' INVENTORS ACHILLE BINCHI BY NGELO MOSTOSI ATTORNEY Aug. 4, 1970 A. BIANcHl ETAL CURRENT LIMITING CIRCUIT BREAKERS 7 Sheets-Sheet 3 Filed Jan. 30, 1968 I NVENTORS HI c NT m BM Y EO W. L

L H.. E 5 MW HG T CN T AA A CURRENT LIMITING CIRCUIT BREAKERS 7 Sheets-Sheet L Filed Jan. 30, 1968 wON H-lo

IN V EN TORS ACHILLE BINCHI ANGELO MOSTOSI JS'Z.

ATTORN EY Aug. 4, 1970 A. BIANcHl ErAL CURRENT LIMITING CIRCUIT BREAKERS 7 Sheets-Sheet i Filed Jan. 30, 1968 NON I N VEN TORS CURRENTv LIMITING CIRCUIT BREAKERS 7 Sheets-Sheet 6 Filed Jan. 30, 1968 wON INVENTORSI ACHILLE BIANCHI- NGELO MOSTOSI og ATTQRNEY A. BIANCH! ETAL Aug. 4, 1970 GURRENT LIMITING cIRcUIT BREAKERS 7 Sheets-Sheet 7 Filed Jan. 30, 1968 INVENTORSI ACHILLE BIANCHI BY NGELO MOSTOSI TTO R N EY United States Patent Of 3,523,261 CURRENT LIMITING CIRCUIT BREAKERS Achille Bianchi and Angelo Mostosi, Bergamo, Italy, assignors, by mesne assignments, to Federal Pacific Electric Company, Newark, NJ., a corporation of Delaware Filed Jan. 30, 1968, Ser. No. 701,721 Claims priority, application Italy, Jan. 30, 1967, 12,055; Nov. 29, 1967, 23,307 Int. Cl. H01h 77/10 U.S. Cl. 335-16 8 Claims ABSTRACT OF THE DISCLOSURE A circuit breaker with high interruption capacity is realized by utilizing an electromagnetic loop that expands instantly when high current develops, to part the contacts initially and to cause continued contact-opening motion to full fault-current interruption. Responsiveness to the electrodynamic force is preserved and adequately large contacts are utilized -without the corresponding consequence of contact-parting bounce at the instant of closing, by providing a gradual contact-closing operation that is completed with a short, sudden motion. In one form, the contact which is operated With minimum bounce to close the circuit breaker is also the contact that is moved electrodynamically to open the breaker; and in this construction the electrodynamic force unlatches the breaker-opening mechanism. In the other form, one contact is actuated to close the contacts and the companion contact is electrodynamically operable for opening the circuit breaker.

The present invention relates to circuit breakers. An object of this invention is to provide circuit breakers of novel construction having relatively high interruption capacity. This capacity is needed where the circuit breaker is connected to an electric bus or cable that is capable of delivering extremely high levels of current under shortcircuit conditions.

A further object of the invention is to provide novel circuit breakers Which can be made in comparatively small physical pr-oportions, which are nevertheless capable of interrupting remarkably high currents in case of shortcircuit.

A still further object of the invention is to provide a novel circuit breaker which will open and safely clear the circuit in response to severe short-circuit, where the shortcircuit exists at the time that the circuit breaker is closed, and also in response to a short-circuit that occurs at some time after the circuit breaker is closed.

The invention has broad application, but it is particularly applicable to circuit breakers of the class having an enclosure of molded insulation. Furthermore, it is particularly applicable to so-called low-voltage circuit breakers, that is, circuit breakers rated at 6010- volts or less.

The novel circuit breakers can be constructed in various physical sizes and with various Operating mechanisms, to open automatically when the current exceeds the overload calibration. Such a circuit breaker may be rated at any value, usually at a value in the range of 15 amperes to 1,.200' amperes. These circuit breakers (of whatever current rating) should have a vastly greater current-interruption capacity.

Two novel forms of circuit breakers in realizing the foregoing objects are represented in the accompanying drawings and described in detail below. In both examples there is a blow-off configuration of the current path to and from the contacts, and in both examples there is an Operating mechanism that closes the contacts in a motion ice that is slow at first and then becomes sudden so that the contacts close firmly and without hesitation.

The blow-off current path includes a current loop which tends to expand mechanically When a short-circuit occurs and this elfect is used to cause instant separation of the contacts.

The high-speed blow-off contact-opening feature is an important factor in providing current-limiting 'Characteristics. Where the circuit breaker opens the circuit fast enough, in a properly proportioned arc chute, the rise of current is limited to only a fraction of the current capacity of the bus. The interruption process is made much easier than in circuit breakers that do not limit the rise of current.

The tendency of the loop to expand is due to the electrodynamic force that develops at the instant that a short circuit occurs. This effect is utilized to cause opening of the contacts under short-circuit conditions. In order to obtain full advantage of the blow-off construction, it is important to avoid ap'preciable mechanical bouncing or rebounding of the contacts as they close. Otherwise the bouncing of the contacts might be a substitute for electrodynamic force in unintentionally causing the contacts to open. Furthermore, bouncing of the contacts Would interfere with the sudden increase in current in case a shortcircuit exists at the time the circuit breaker is closed, and interference with the current rise would interfere with the electrodynamic contact-opening force that is needed to limit the rise of current. The novel circuit breakers are operated into closed position with firm closing force by a mechanism that operates the -moving contacts gradually through most of the closing stroke, followed by a sudden short motion that completes the closing of the contacts, without interfering with the electrodynamic contact-opening feature.

One of the circuit breakers described below is especially adapted to operate at relatively high rated-current levels, and to -withstand particularly high short-circuit current levels. The cnrrent-carrying parts -are made large, to handle the high rated currents. The contact Structures and the electrodynamic release mechanism in this circuit breaker for causing the contacts to open involve further novel features of the invention.

Pursuant to one feature of this form of circuit breaker, the moving contact is made of two parts, a main contact part and an arcing contact part. When the circuit breaker is in its closed condition, the main contact part is pressed firrnly against the companion contact. In case of a shortcircuit the electrodynamic force developed by the reversecurrent loop acts to lift the main contact part. High contact pressure is maintained and even increased at the arcing contact part. The arrangement is such that the arcing contact will not break the circuit unless the electrodynamic force is great enough to release a latch which restrains a spring-biased contact-opening mechanism. When the mechanism is released, the circuit breaker opens at high speed, far enough to clear the circuit. The electrodynamic force first unlatches the contact-opening mechanism and then the electrodynamic force directly increases the contact-opening force of the contact-opening spring. Because the arcing contacts remain closed until the opening mechanism is unlatched there is no possibility of small arcs developing between contacts that open slightly and then close again. Without this feature, such a condition could exist in case of large currents that are not large enough to release the opening mechanism. The arcing could damage the contact surfaces, and could result in the contacts becoming welded together.

Circuit breakers of this construction operate in the contact opening direction With a great deal of speed. The

moving contact structures of such crcuit breakers are massive when designed to carry high currents. A massive moving contact structure having a high contact-opening speed normally tends to rebound powerfully in the contact-closing direction as soon as it reaches the limit of the opening motion. A further features of this invention resides in providing a simple, effective and reliable antirebound latch for the moving contact structure.

In the second form of current-lirniting crcuit breaker there is also a blow-off configuration of the current path to and from the contacts, and there is also an operating mechanism that closes the contacts in a motion that is slow at first and then becomes sudden so that the contacts close firmly and without hesitation. Certain additional objects and advantages are realized in the second embodirnent. A maximum separation of the contacts is realzed, an advantage in assuring reliable interruption of the arc under all conditions. Also, even though it is possible for only one pole of the crcuit breaker to open electrodynamically (due to short-crcuit current in only one pole) nevertheless there is provided a reset mechanism that guarantees closing of the contacts in all the poles when the crcuit breaker is operated subsequently.

The foregoing general discussion of some of the novel features of the invention will be understood better by considering the drawings and the following detailed description.

In the drawings:

FIG. 1 is a lateral cross section through the center pole of a multipole circuit breaker involving one embodiment of certain features of the invention, the crcuit breaker being shown With the contacts open;

FIG. 2 is a fragmentary cross section of the crcuit breaker in FIG. 1 With the contacts shown closed, and With antirebound latching parts shown in broken lines to represent an instantaneous relationship thereof during opening of the breaker;

FIG. 3 is another fragmentary cross sectional view of the crcuit breaker in FIG. l illustrating certain parts while under the influence of electrodynamic force and including a manual operating lever in broken lines;

FIG. 4 is a plan view, partly in cross section, of a second circuit breaker constituting another illustrative embodiment of certain aspects of the invention;

FIG. 5 is a vertical cross section of the circuit breaker viewed from the plane 5-5 in FIG. 4 with portions thereof shown in broken lines to illustrate the positions thereof assumed during a short-crcuit interrupting operation;

FIG. 6 is a bottom view of the crcuit breaker in FIGS. 4 and 5 as seen with a cover removed; and

FIG. 7 is a lateral view of the Operating mechanism as viewed from the plane 7-7 in FIG. 5.

The crcuit breaker shown in FIGS. 1 to 3 includes an enclosure or case formed of parts of molded insulation including parts 10 and 12. Part 10 contains an arc chute 14 which has side walls 16 and end wall 18 of fibre or other suitable arc resistant insulating material, supporting an assembly of V-notched arc splitter plates 19 of magnetizable metal. The arc chute and part 10' of the molded enclosure have a vent opening 20 Which is shielded by a wire-mesh barrier 22 Secured in grooves in molded part 10.

The electric crcuit through the illustrated pole of the crcuit breaker includes a terminal 24 and an elongated conductor 26 carrying stationary contact structure 27 comprising stationary main contact 28 and stationary arcing contact 30. Arcing horn 32 extends from contact 30 into arc chute 14. Movable contact member 34 yincludes a main contact part 36 and an arcing contact part 38. Elements 28, 30, 36 and 38 are of suitable material such as silver-tungsten. A flexible elongated conductor 40* as of laminated copper, provides a current path from movable contact member 34 to a fixed block 42, and to terminal 44.

In the closed condition of the crcuit breaker (see FIG. 2) a current loop is formed of conductor 40, movable contact 34, the companion contact 27 and conductor 26. Conductors 26 and 40 carry currents in opposite directions, and are called reverse current paths. These parts repel each other electrodynamically when they carry current.

Movable contact 34 is carried by an arm or contact carrier 46 which is essentially channel shaped, opening downward. Arm 46 is pivoted on a supporting shaft 48 which extends through the side walls 50 of the channel. A compression spring 52 (FIG. 2) on guide rod 57 works against pivot 56 on contact carrier 46, and the opposite end of this spring presses against a fixed pin 54. Multiple Springs like spring 52 may be used at opposite sides of the mechanism, only one spring being shown. Pivot 56 of spring 52 approaches the line of centers of pin 54 and shaft 48 as the contacts close, but pivot 56 does not reach this line of centers. Spring 52 provides opening bias for arm 46 about shaft 48 when the arm is in its open position. When arm 46 is in the contacts-closed position, spring 52 is compressed further, but the opening force is not greatly increased because the line of the spring force is closed to pivot 48.

The Operating mechanism for arm 46 includes a link 58 having one end pivoted to arm 46 and having a pin 60 at its opposite end. Pin 60 moves in a slot 62a of another link 62. Pin 60 also carries a roller 64 (see FIG. 3).

A heavy triangular Operating member 66 is fixed to a stationary shaft 68 rotatably mounted in side plates 69. There are two side plates 69 at opposite sides of the mechanism. Shaft 70 extends into slots 71 in the side plates. Movement of shaft 70 to the right is limited by the right-hand ends of slots 71. Shaft 68 is rotated and member 66 is operated to the right and to the left for opening and closing the crcuit, by means that is diagrammatcally represented in FIG. 3. As shown there, a manual lever 73 has a large opening 7311. that receives shaft 70 to drive the pin in each direction. The arrangement is such that shaft 70 is not restrained and can overtravel When snapping operation occurs, as Will be described.

Shaft 70 connects member 66 to link 62. Compression spring 72 has a guide rod 74 whose slot 74a works along fiXed pin 76. Pin 78 connects the opposite end of guide rod 74 to member 66.

Latch member 80 is pivoted on shaft 68 and has an upper edge portion 80a (FIG. 3) that is engaged by shaft 70 in the open condition of the crcuit breaker (FIG. 1). Latch member 80 has a latch portion 80c that is pressed down under a hook portion 82a. of latch 82 -when the circuit breaker is open, for relatching. Latch 82 restrains latch member -80 when the crcuit breaker is closed. Member "80 also has an edge 80d constituting a bearing rail for roller 64. A slight depression 80e in member 80 establishes a stable end position in the leftward travel of roller 64, so that the roller is arrested in the position illustrated in FIG. 3 when the crcuit breaker is closed.

Latch 82 is carried on a fixed pivot 84 and has an arm carrying a pin 86. Rod 88 has a slotted upper portion which receives pin 86; best shown in FIG. 3. The lower end of rod 88 is cylindrical and it is threaded, and it terminates in a slotted portion Which fits about pin 98. Compression spring 90 on rod 88 is confined between pin 86 and a nut 92 adjustable on rod 88. Another nut 94 on rod 88 provides an adjustable lower end for rod 88 to bear against pin 98. Nuts 92 and 94 have many notches around their edges, and these nuts are held in any adjusted position by bending a tongue 96a of washer 96 into such notches.

Pin 98 is carried by a latch part 100 which moves about a pivot 102. In FIG. 1 pin 98 is shown slightly to the right of a line between the centers of pivots 86 and 102. Spring 90 normally maintains pins 98 and 86 in the extended condition illustrated so that parts 86, 88, 90, 92, 94 and 96 act as if they were a simple link under normal conditions. This link transmits a force from latched member -80 pressing latch 82 clockwise (FIG. 2) to apply latch pressure of latched part 100 against latch 104.

|Latch 104 has an arm 104a that can be lifted by upward movement of bimetal 108. Independently, latch arm 104a is operable by upward movement of a rod 110 that is slidable in a bore in member 26. A 4U-shaped soft iron core 114 extends across the top of conductor 26 and has downward extending legs. Opposite core 114 is a soft iron armature 112a carried by a pivoted arm 112.

A persistent moderate overcurrent in conductor 26 causes heating sufficient to deflect bimetal 108 upwardly for releasing latch parts 100 and 104.

Bimetal r108 has a support pivot 1089: and an adjusting structure 108b for externally accessible adjustment of the "thermal tripping-current level. In the event of a more severe overcurrent, armature 112a is lifted so that pin 110 pushes arm 104a. to release latch 104 and latch parts 100 in response to magnetic tripping-current levels. In case of either magnetic tripping or a thermal tripping, latch 104 swings clockwise to release latched part 100. Thereafter the parts 88-90-92-94-96-98 act as a unit to swing latch part -100 clockwise about its pivot. Release of latch 104 releases latched part 80 (FIG. 2) and this allows link 58 and the entire contact assembly to swing upward due to the bias of contact-pressure spring 126 and, thereafter, compression spring 52. Reset of latched part 80 is accomplished by clockwise rotation of triangular 'member 66, Which drives shaft 70 against the portion 80a of part 80, returning the mechanism to the configuration in FIG. 1. Latch 82 and unit l88 98 and 100 are reset by the bias of tension spring 116'which engages latched part 100 (FIG. 1). Latch 104 is reset by a suitable weak spring (not shown).

Moving contact 34 has two pins 120 and 124. Pin 124 is received in a pair of slots 122a in a downward-facing channel element 122. Moving contact 34 is biased down- Ward by compression spring 126. A pair of links 118 pivoted to shaft 48 support pin 120, and links 118 are arrested (against bias of spring 126) by stop 127 fixed to the side Walls 50 of downWard-facing channel 46.

Spring 126 bears against contact34 between the two pins 120 and 124. In the closed condition of the contacts, both contact parts 36 and 38 bear against the companion contacts 28 and 30, pin 124 being spaced away from the lower edges of slots 12211. In the closing motion of contact 34, contact part 38 engages contact part 30 first and the main contacts 36 and 28 engage thereafter. In the opening motion, contact parts 28 and 36 separate first sothat arcing occurs only at parts 30 and 38. t

When the circuit breaker is closed, a current loop is provided by conductor' 26, contacts 27 and 34, and flexible conductor 40. The current loop includes reverse current paths in parts 26 and 40. In case of a short circuit, this current loop tends to expand under lenormous electrodynamic force, and the parts assume the configuration in FIG. 3 almost instantantly. Flexible conductor 40 lifts contact 36. Links 118 as Well as conductor 40 bear against channel 46 With great force. During this motion spring 126 continues to exert great downward force, maintaining contact at arcing contacts 30 and 38. The electrodynamic force pushes contact arm 46 upward against link 58, applying apowerful bias to lift member 80, but no motion of arm 46 has occurred thus far.

There is a slight push-off angle at engagement point 800, 82a, Which provides an enormous reverse mechanical advantage." This means that a very large upward force applied by member 80 to latch 82 causes only a very small force tending to rotate latch 80 clockwise. This force is opposed by spring 88 acting on latch 82. When the electrodynamic force (greatly reduced by the elfect of the push-off angle at 800, 8211) overcomes the restraining effect of spring 88 on latch 82 (see FIG. 3),

latched part is released and the contact arm 46 is driven upward electrodynamically at high speed. There,

is no delay in the unlatching operation, only a measuring of the opening force as against the required unlatching force. If the force is not adequate to release latch 82, contact part 36 may lift somewhat. No arcing occurs,

inasmuch as arcing contact part 38 firmly maintains a' circuit between moving contact 34 and companion contact 26 until the latch 82 is released.

In case the contact arm should be released and driven upward there is danger of impact at its upward limit followed by rebound downward toward the companion contact 26. To avoid any such effect, an antirebound latch 128 is provided having a tail 128a that is struck by a hooked part 130 at the top of contact arm 46. This drives latch 128 into dotted-liue position in FIG. 2. Part 130 is hooked by latch 128 and prevents arm 46 from rebounding downward. When the breaker is closed spring 133 biases tail v12811 to an advanced position as shown in solid lines in FIG. 2 slightly clockwise of the position of FIG. 1, so as to be struck by part 130 when the arm 46 comes close to its full-open position.

The foregoing circuit breaker is operative as a single pole device or with multiple poles tied together and linked by mechanically coupled trip units, in various Ways Well known in the art.

When Operating member l66 is being moved from the position in FIG. 1 to that in FIG. 2, link 62 intially draws shaft 60 toward the left and progressively drives link 58 in the direction to swing contact arm 46 down- Ward. As this motion continues, pivot 78 swings upward about shaft 68 and approaches the lines of centers of shaft 68 and pin 76. Shortly after pin 78 passes this line of centers, spring 72 provides an abrupt further motion to member 66 in the counterclockwise direction, thereby Suddenly completing the travel of pin 60 to drive roller 464 to the position shown in FIG. 3.

The circuit breaker illustrated is of a physical design suitable for carrying large amounts of rated current, for example, 1000 amperes, and accordingly the various current carrying parts may well be relatively large and massive. Consequently, when the circuit breaker is being closed there would be a tendency of the movable contact arm to rebound after striking the companion contact structure 26. Such a rebound involves an up- Ward reaction force tending to release the latch 82 from latched part 80, in this manner simulating the electrodynamic force that develops when the circuit breaker is subjected to high levels of short-circuit current. Such large impact and rebound forces are avoided here by virtue of the action of the contact-closing mechanism described above which operates in the closing direction to carry the movable contact structure gradually through most .of its Operating stroke. The completion of the closing stroke is accomplished suddenly when |pin 78 crosses the line of centers between shaft 68 and pin 76. Thus the contact-closing motion is completed with a short sudden motion and the contact-closing operation is firm and without hesitation.

The action of the electrodynamic force which occurs under short circuit conditions may develop at a time when the circuit breaker has been closed or it may exisit before the circuit breaker is operated to close the contacts. In any case, the sudden appearance of the electrodynamic force is such that contact opening motion is extremely fast, occurring during the sudden rise of the shortcircuit current. This operation takes place within a small part of a half-wave, in the case of 60-cycle alternatingcurrent circuits. With a properly proportioned arc chute, current interruption occurs in such a manner as to limit the rise of current well below anything that might be expected in circuit breakers of other construction, in Which no current li-miting action occurs. As a result the interruption process does not await the normal end of the half-cycle during w-hich contact opening occurred.

aszazsi Instead the arc is suppressed and the current is'interrupted before waiting for the alternating current wave to pass through zero.

Referring now to FIGS. 4 to 7, another form of circuit breaker is shown as a second illustrative embodiment of certain features of the invention found in the circuit breaker of FIGS. 1 to 3 and including additional novel features. In FIG. 4 the circuit breaker shown involves three side-by-side poles having an arc chute 200 and a pair of terminals 202 and 204 in each pole; and at one end of the unit there is an Operating mechanism generally designated 206. The circuit breaker is divided into a current-interrupting unit 208 which includes the arc chutes and the separable contacts (to be described) and the Operating mechanism, plus a second unit 210 which includes the overload sensing devices for the respective poles, and a coupling arrangement to control the operating mechanism 206.

Section 208 (FIG. 5) includes a housing portion 212 of insulation containing an arc chute involving a fibre "wrapper 214 and a plurality of ferrous V-notched arc splitter plates 216. A movable contact arm 218 is shown in its fully closed position, held in this position by shaft 220. This shaft is common to all of the poles and is insulated from each of the contact arms 218. A companion contact arm 222 on pivot 224, individual to each pole, is biased by a compression coil spring 226 in the closing direction so that contacts 228 and 230 are in firm pressure contact with each other. In this condition, both contact arms 218 and 222 are out of engagement with a dividing wall 232 of insulation, integral with housing 212. Coil spring 226 is guided along a metal strip 227. One end of the spring presses against a disc 227a fixed to strip 227, and the other end of spring 226 presses against bracket 229. Strip 227 slides loosely in a slot in bracket 229. The other end of strip 227 is pressed into a notch 223 in arm 222. In the closed condition of the contacts, spring 226 acts on strip 227 along a line that passes above pivot 224 and in this way spring 226 provides firm contact pressure.

The overload sensing structure 210 in each pole includes a bimetal 234 which moves to the right When heated by a current-carrying conductor 236 of limited cross section. An overcurrent deflects bimetal 234 to the right sufiiciently to operate trip lever 238 about common trip bar 240. This trip bar extends to the mechanism 206. A magnetic core 242 having a transverse portion encircled by conductor 236 is disposed to attract an armature 243 in the event of sudden high levels of overcurrent well above the tripping level of bimetal 234. Motion of armature 243 is resisted by a coil spring 244. When there is a sufiicient overcurrent, armature 242 moves to the right and operates trip bar 240.

A circuit may be traced through the pole represented in FIG. 5 starting at terminal 204, through conductor 236, conductive stud 246, and a flexible conductor 248, through contact arms 218 and 222, then through flexible conductor 249, to opposite terminal 202.

In the event of a mild overload, bimetal 234 deflects trip bar 240 after a substantial delay (depending on the severity Of the overcurrent) and for higher levels of excess current, armature 243 operates trip bar 240 in the tripping direction, with faster response.

In the event of a sudden current of short circuit proportions, the current loop extending through arm 218, contacts 228 and 230, and arm 222 constitutes an electrodynamic loop tending to drive arm 222 clockwise about its pivot 224. At this time contact arm 218 is mechanically held in the closed position by the Operating mechanism 206. However, the force of spring 226 is overcome by the electrodynamic force, and arm 222 moves toward its dotted-line position. As this happens, the line of action of spring 226 changes. At one moment this line extends through pivot 224, which is a centered position. From the start until this moment, the compression of spring 226 ncreases but the effective force of the spring in the contact-closing direction decreases and becomes zero when strip 227 extends along a line through pivot 224. The inertia of arm 222 which is in motion, and a residual amount of electrodynamic force, carry spring 226 past the centered position and then spring 226 forces arm 222 to complete the opening motion to stop 260. This is a second stable testing position of arm 222.

When the short-circuit appears, armature 243 drives trip bar 238 in the direction to release the Operating mehcanism of contact arm 218, and this arm moves to its dotted-line position. This occurs after a short delay following the high-speed motion of contact arm 222. The great separation between contact arms 218 and 222 in their dotted-line positions provides a further guarantee that any persisting arc will be interrupted.

FIGS. 5 to 7 show the Operating mechanism for contact arm 218, and also show two additional features, (1) the mechanism for resetting arms 222 to prepare the circuit breaker for reclosing, and (2) a mechanical arrangement for tripping the circuit breaker in case any arm 222 is opened electrodynamically.

Each of the contact-carrying arms 222 has an extension 222a acting on an insulating material plate 250 (FIG. 6) which is freely slidable between the rollers 256, the latter being pivoted on fixed aXes, and guided by flat surfaces 262 and 264.

Said plate 250 has a slot 2S0a receiving the extension 206aof the manual Operating lever of' the breaker.

When at least one contact-carrying arm 222 is rotated clockwise by electrodynamic forces, its extension 222a acts upon the plate 250 and shifts the latter to the position shown in dotted lines, overcoming the bias of the spring 254.

During progress of said shift, the plate 250, by means of its extension 25017, induces the rotation of lever 252 and the latter, via a linking mechanism which is shown in FIG. 7, acts like trip bar 240 on a latching mechanism described below, and thus opens the circuit breaker.

The contact 228 is thus brought to the position shown in dotted lines. Concurrently, the Operating lever of the circuit breaker, set free by the trip mechanism, is brought to the upper end of the slot 250a, a position connoted 'by EGT."

Said position of the Operating lever, intermediate between those taken as the circuit breaker is open 0" and closed I, indicates that the circuit breaker has been opened by automatic release action. See FIGS. 4 and 6.

To restore the contacts 230 to their position shown in solid lines part 206a of the manual Operating lever is moved to the open breaker position O.

In so doing, the Operating mechanism is reset and, concurrently, the extension 20-6a is moved and shifts the plate 250. The latter, in turn, moves the extensions 222a of the contact-carrying arms 222 so that contacts 230 are brought back to their position as shown in solid lines in FIG. 5.

The circuit breaker cannot be closed if even a single contact of the contacts 230 is in the position indicated in dotted lines, since the two actions, relatching of the Operating mechanism and moving the contacts 230 to the position required for closing the circuit breaker take place simultaneously.

In the case of a very high overcurrent, electrodynamic forces develop in the loop formed by arm 218, contacts 228-230 and arm 222, which tend to swing the arm 222 clockwise about its pivot 224. At this stage the contactcarrying arm 218 is mechanically retained in the closed position by the Operating mechanism 206. When the electrodynamic forces are such as to overcome the contrary bias of spring 226, the arm 222 is rotated clockwise and the contacts 230 are driven away from the contacts 228.

The separation of the contacts and of the contactcarrying arms gives rise to a decrease in the electrodynamic forces acting on the arms 218 and 222. Said decrease is countered, at least in the first stage of movement, by the fact that the current is still increasing under usual short-circuit conditions, in spite of the insertion in the loop of the resistance due to the arc. f

'Simultaneously,- as has ybeen seen, there is a decrease of the counter-torque due to the spring 226: 'for this reason, the movement of the arm 222, once it has been started, is irreversible, and the contact 230 is stopped only when it reaches the second equilibrium position as determined by the abutment 260.

As has been observed, the clockwise rotation even of a single one of the arms 222 also causes the opening of all the contacts 228.

The result is that, as a consequence of an abrupt overcurrent, both the contacts 228 and 230 take the position shown in dotted lines.

FIG. 7 shows details of a suitable Operating mechanism for contact arms 218 on shaft 220, and for elements 206a and 252 in FIG. 6. Note that FIG. 7 shows 'the mechanism in the open condition of the 'circuit breaker. Manual lever 206b has a fixed pivot 265 in metal frame 266. Lever 206b drives link 268 to operate a secondary operating lever 270 about a hearing o'n shaft 220 but lever 270 does not operate shaft 220 directly.

Arm 272 fixed to shaft 220 is pivoted to a toggle link 274. Another toggle link 276 is pivoted to link 274 at the knee of the toggle, and a roller 278 is carried on this pivot. The upper end of link 276 is pivoted to aj member 280, which has a fixed pivot 282 in the frame. Tension coil spring 284 hooks on a pin 286 on manual level 206b, and spring 284 biases the knee of the toggle upward.

This linkage is shown in the normal open position of the circuit breaker. To close the circuit breaker, manual lever 206b'is moved to the right. A part 27011 of secondary lever 270 reaches roller 278 and pushes this roller, in the direction to straighten toggle links 274 and 276, and driving arm 272 and the contact-arm shaft 220 in the closing direction gradually. During this motion of manual lever 206b, spring 284 gradually changesits line of action until this line crosses the top pivot 288 of the toggle. After that point is passed, the toggle is operated by spring 284 in a sudden motion, moving roller 278 away from part 27011. Contacts 228 close Suddenly against contacts 230. This gradual motion of the contact arms 218 through most of the closing stroke, followed by a sudden but short motion to complete the closing stroke, is important for preventing bouncing of the contact arms 222 as already explained.

FIG. 7 shows trip arm 238a that is operated by bimetal 234 or armature 243 (FIG. in case of an overload. Arm 238a moves tothe right for tripping the circuit breaker, and operates secondary latch 290 on its pivot 290a, and releases latch 292 to release member 2810 in the usual manner. Toggle spring 284 can then cause arm 272 to open the contacts. Later, manual level 206b is forced toward the left to operate reset pin 294 for resetting parts 280, 292 and 290 to the condition shown, the described release mechanism and contact-opening mechanism is entirely conventional.

FIG. 7 shows the connection of extension 206a (FIG. 6) to the manual lever 206b. When the top of lever 206b moves to the right to close the circuit breaker, extension 206a moves freely in slot 250a. Later, in case any one of the contact arms 222 open electrodynamically, plate 250 is shifted to the left in FIG. 7 and strikes lever 252.,This operates another lever 298, to release latch 290. So long as any arm 222 remains in its open'flposition, plate 250 and lever 252 act to prevent relatching of the circuit breaker, as previously explained in connection with FIG. 6. This arrangement prevents a dangerous condition. To reset arms 222 it is only necessary to move manual lever 206b in the direction to reset the latch mechanism, because in this motion tail 206a drives plate 250 in the direction to reset contact arms 222. It is notable that this arrangement provides for resetting of arms 222 without in any way interfering With the maximum open condition of the contact arms 218 and 222 as shown by dotted lines in FIG. 5. Plate 250 is a mechancal coupling to the automatic release mechanism of the circuit breaker, and is important because it assures opening of all the contacts 228 in case of a short circuit. Plate 250 supplements the action of armature 243. In case no armature or bimetal is used, plate 250 is the only automatic control for releasing all .the contacts 228 to open when any one or more of the contacts 230 are opened electrodynamically.

What we claim is:

1. A circuit breaker of high interrupting capacity, including a pair of terminals and means including almovable contact and a companion contact providing a current path interconnecting said terminals, andmechansm for Operating the movable contact to open and close the circuit breaker, characterized in that said current path includes a blow-open loop tending instantly to enforce opening movement of one of the contacts by electrodynamic force in response to sudden high levels of current, said circuit breaker having means normally effective when the circuit breaker is closed to hold the contacts closed and said means being operable by said electrodynamic force for causing opening operation of the circuit breaker to its current-interrupting configuration, and further characterized in that said mechanism for Operating said movable contact includes means for Operating the movable contact gradually in the contact-closing direction followed by a short sudden contact-closing motion, for quickly and firmly closing the contacts with a minimum of mechancal bounce and thereby avoiding interference with the operation of the blow-open current loop.

2. A circuit breaker in accordance with claim 1, further characterized in that the movable contact includes an arcing contact part and a main contact part, the latter normally being pressed against the companion contact, said blow-off loop being arranged to lift the main contact part by electrodynamic force, and means for converting the electrodynamic force that lifts the main contact part into a force that presses' the arcing contact part against the companion contact.

3. A circuit breaker in accordance with claim 2, in which the circuit breaker includes companion main contact parts and companion arcing contact parts, further characterized in that the Operating mechanism includes a contact-opening spring and a latch that is releasable by expansion of the blow-off loop for causing continued opening movement of the main contact part and instantly causing high-speed openingfof the arcing contact part.

4. A circuit breaker in accordance with claim 1, wherein the contact that is moved electrodynamically has a means for holding it in its open position, and wherein the operating mechanism has an instantaneous release mechanism to move the other contact to its open position so that both contacts move away from their closed positions in case of short circuit.

5. A circuit breaker in accordance with claim 4, Wherein said automatic release mechanism has a mechancal coupling to the electrodynamically operated contact for insuring release operation.

6. An automatic circuit breaker in accordance with claim 4, including means for resetting said electrodynamically operated contacts and additionally for resetting the automatic release mechanism of the circuit breaker.

7. A circuit breaker in accordance with claim 1 including a latch having a hook portion cooperable with the moving contact structure thereof to arrest return motion thereof toward the companion contact and a biasing spring normally holding the hook portion out of such cooperation, said latch having a portion disposed to be struck by the moving contact structure as the limit of its opening motion is reached for impelling the hook portion into position to arrest the moving contact structure against said return motion.

8. A circuit breaker in accordance with claim 3 including a latch having a hook portion cooperable With the moving contact structure thereof to arrest return motion thereof toward the companion contact and a biasing spring normally holding the hook portion out of such cooperation, said latch having a portion disposed to be struck by the moving contact structure as the limit of its opening motion is reached for impelling the hook portion into position to arrest the moving contact structure against said return motion.

12 1 References Cited v .UNITED srATEs PATENrs 3,127,4ss

3/1964 Bodensehatz 33s 16 3,134,-s79 5/1964 Gauthier zoo-169 3,299,2443 1/1967 snwbelv 2oo 169 v FOREIGN PATENTS t- 1,3ss,664 1/1965 France.

m BERNARD A. GILHEANY, Primary Examiner Hr BROOME, Assistant Examiner 

